question on injector maximum duty cycle and dual injectors

[Yves]

The following : car is equiped with a SBC, basically a short stroke big bore unit with ported heads and ITB intake (crossram) with dual plenums to feed the stacks. The car is made to run higher rpm's with a designed (!) redline of 7800. Springs allow for at least 8000. I have only taken her up to 6750 at this point as high rpm and high kPa area in that zone is not fully tuned and because roads in my neighborhood are kind of limited.

Anyway. I was going over my old log more specifically the one where I had her up to 6750. Injector duty cycle there was 67.5%. I run Ford Motorsports 42 lbs injectors with a fuel pressure of 45 psi.

I have a idle AFR fluctuation that can vary within 1-1.5 point. Not sure if this is due to the cam (247/249 @ .050) or because my injector dead time isn't correctly set. Could also be the injectors are too big for a finely adjusted idle or because due to the way the injectors are mounted on this intake (90° into the airstream) is not ideal.

As I'm reaching 67% duty cycle at an rpm below my redline I was wondering if these would be enough to feed the engine higher. Still have some 13-18 duty cycle left. With some difficulty I could mount a second injector in the airboxes that inject into the stack mouth and mount say 18-15 lbs injectors in place where the 44 lbs are now (close to the head port).

To note is that I need to do some rewiring since I had issues with intermittently bad contacts on the ampseal connector I used on the engine as quick disconnect.

What's the opinion here ?

[BigLou240sx]

Assuming you want the same AFR at 7800 as you had at 6750, and VE at 7800 = VE at 6750 (VE at 7800 will likely be lower than at 6750 unless your torque peaks higher than I'm thinking), a 67.5% duty cycle at 6750 translates to a 78% duty cycle at 7800. This is still below the recommended duty cycle limit of 85%